Antenna construction for mobile communication unit



Aug. 9, 1966 E MAHONEY ET AL 3,266,042

ANTENNA CONSTRUCTION FOR MOBILE COMMUNICATION UNIT Filed April 2. 1964 2 Sheets-Sheet 1 FIG. 2

FIG. 5 I6 INVENTORS:

EDWARD H. MAHONEY PAUL E. KNIGHT ATT'YS 1966 E. H. MAHONEY ET AL 3,266,042

ANTENNA CONSTRUCTION FOR MOBILE COMMUNICATION UNIT Filed April 2, 1964 2 Sheets$heet 2 In MM S m0 m HT T V AH M m Mm HN K D RE L Mm EDu United States Patent 3,266,042 ANTENNA CQNSTRUCTEON FOR MGBILE CUMIVIUNICATEGN UNIT Edward H. Mulroney and Paul Eugene Knight, Tulsa, 01th., assignors to Seismograph Service Corporation, Tulsa, Okla, a corporation of Delaware Filed Apr. 2, 1964, Ser. No. 356,912 22 Claims. (Cl. 343-718) The present invention relates generally to a combined hat and antenna construction for a mobile communication unit and is more particularly concerned with a unit of this type which may be readily worn by a person carrying radio equipment for communicating with other similar mobile stations or with one or more fixed stations.

The present invention is useful in communication systems of the type disclosed in copending U.S. application Serial No. 156,351 filed on December 1, 1961 by Clyde Hussey and assigned to the same assignee as the present invention, now US. Patent No. 3,191,122. As is described in detail in the latter application, such systems comprise one or more master or relay stations for transmitting radio signals to and receiving signals from a plurality of remote units which are preferably portable.

In some operations it is desirable to free the hands of the operator at the mobile station to permit him to perform other tasks or duties and, in this event, the radio equipment including the antenna is often worn by the operator or strapped to his body. The antenna often takes the form of a vertically extending rod which creates a safety hazard in view of the possibility of engaging power lines or equipment in the area. Moreover such an antenna is highly inconvenient to the operator particularly in crowded areas Where he must remember to keep the antenna free from obstacles. In order to minimize these problems, the height of the antenna is usually limited but, since maximum performance is achieved when the antenna is a quarter wavelength of the operating frequency, a reduction in height represents a decided compromise with performance characteristics. Reduction of the height of the vertical antenna below a quarter wavelength reduces the colinear aperture of the antenna with a resulting loss in radiation resistance and a decrease in the energy coupled to or from space. In accordance with the present invention, these problems are overcome by providing an antenna in the form of a discontinuous halo or partially open ring lying below the crown or peak of a helmet worn by the operator at the mobile station, thus avoiding the use of an upwardly extending antenna. The helmet itself is constructed to provide a ground plane for improving the gain of the antenna.

Accordingly, the invention has for its primary object the provision of a new and improved hat or helmet having an open antenna ring mounted thereon in a position below the peak or crown of the helmet.

Another object of the invention is to provide a new and improved helmet construction including novel means for making electrical connections to the ring antenna.

A further object of the invention is to provide a new and improved helmet construction having standoff supports for the antenna ring wherein certain of these supports are so spaced and constructed that they also serve to permit electrical connections to be made to the antenna ring.

Theinvention has for another object the provision of a new and improved helmet of the character described above wherein the ground plane is formed by plating at least a portion of one surface of the helmet with a conductor.

The invention has for a further object the provision Patented August 9, 1%66 'ice of a new and improved helmet construction of the type described wherein the antenna ring and the ground plane are formed by plating rings on one of more surfaces of the helmet, thus providing a simple, inexpensive and trouble-free unit.

In accordance with the present invention, the foregoing and other objects are accomplished by a helmet construction having an antenna in the form of an open ring disposed below the peak or crown of the helmet. The helmet is also provided with means forming a ground plane for the antenna and one end of the ring is grounded. If the helmet size and the frequencies allocated permit, the antenna ring may be self resonant, that is, it may be made approximately one-quarter wavelength of the operating frequency. However, since frequencies usual-1y allocated for communication system of the type disclosed in the above-identified copending application Serial No. 156,351 are in the range of 26 to 31 megacycles it is generally impractical to make the ring long enough to be self resonant. Therefore, an adjustable air capacitor may be connected between the other or open end of the ring and the ground plane to permit tuning to electrical resonance. The grounded end of the antenna ring serves as the feed end. Impedance matching between the antenna and the transmitting and receiving equipment of the mobile station is achieved by a so-called gamma match comprising a short section of the antenna ring cooperating with the ground plane to form an open wire transmission line. The feed point to the ring is determined by the feed line impedance and is selected to maintain the match over a two to one frequency range.

In one form of the invention the helmet is of a conducting metal forming the ground plane for the antenna which is in the form of a partially open ring mounted upon a plurality of spaced apart standoff supports. The ring extends through a housing mounted on the exterior of the helmet and containing the tuning capacitor which is connected between the end of the ring and the ground plane. The remaining end of the ring is directly connected to the ground plane within the housing. One of the standofi" supports is spaced from the housing by the distance required to achieve the impedance match described above. The feed connection from the antenna ring to a coaxial line leading to the transmission and receiving equipment is made through the latter support.

In a second form of the invention, the ground plane is formed on the interior surface of the helmet which is preferably formed of a hard, molded plastic. The ground plane loop is preferably formed by electroplating a copper layer onto an area of conducting paint on the plastic base.

In a third form of the invention, the antenna ring with the discontinuity therein is formed on one surface of the helmet and a ground plane in the form of a closed loop is formed either on the latter surface or on the opposite surface of the helmet. Both the closed loop and the discontinuous ring are preferably formed by cooper plating over strips of conducting paint applied on the areas to be plated.

In a fourth form of the invention the discontinuous antenna ring and the ground plane are formed as an integral unit for ready assembly upon helmets or hats already in the field.

The invention, both as to its organization and manner of operation together with further objects and advantages will best be understood by reference to the following deta led description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a side elevational view illustrating a combined helmet and antenna construction characterized by the features of the present invention;

FIG. 2 ,is a top plan view of the helmet and antenna unit shown in FIG. 1;

FIG. 3 is an enlarged, fragmentary sectional view taken along a line substantially corresponding to the line 3-3 in FIG. 1 and showing particularly the housing for the tuning capacitor;

FIG. 4 is an enlarged, fragmentary, sectional view taken along a line substantially corresponding to the line 44 in FIG. 2 and showing particularly the feed connection to the partially open antenna ring;

FIG. 5 is a schematic diagram showing the equivalent electrical circuit of the antenna unit shown in FIGS. 1 to 4;

FIG. 6 is a view similar to FIG. 1 but shows a combined helmet and antenna unit having a ground plane formed by plating on the interior surface of the helmet;

FIG. 7 is a fragmentary view showing the interior of a helmet like that shown in FIG. 1 but with the ground plane formed as a closed loop on the interior of the helmet and with the partially open halo or antenna ring also being formed on the interior of the helmet; and

FIG. 8 is a perspective view showing a helmet and a combined antenna and ground plane unit which may be readily mounted on the helmet.

Referring now to the drawings and first to FIGS. 1 to 5 the present invention is there illustrated as comprising a helmet 10 having an open bottom 11 and a peak or crown portion 12. The particular shape of the helmet is of no significance insofar as the present invention is concerned since it is merely designed to provide the desired protection against head injuries to the wearer. The hat may be made in different sizes to fit the operator at the mobile station. Preferably, the helmet is formed of a conducting metal forming a ground plane indicated by the reference numeral 13 in FIG. 5.

An antenna 16 formed by a discontinuous conducting ring is carriedby the helmet 10 at a position well below the peak or crown 12 of the helmet in order to avoid the aforementioned safety hazards and to provide a ring of substantial size to improve the operating characteristics of the antenna. Preferably, the ring is formed by a tube of a conducting material bent to form a partially open or discontinuous halo which is illustrated as being somewhat egg-shaped in view of the non-circular configuration of the helmet. The ring may be self-resonant, that is, it may have a length of approximately one-quarter wavelength of the operating frequency of the system and, if the ring were circular, this would be accomplished by forming the antenna with a diameter of 28 electrical degrees at the operating frequency. It is desirable that the antenna ring 16 be spaced from the ground plane 13 by a distance equal to approximately 2.5 electrical degrees or less at the operating wavelength and, to this end, the antenna is mounted upon four spaced standoff supports 17, 13, 19 and which are of proper length to provide the indicated spacing. The standoifs 17, 18 and 19 are of identical construction and each comprises an insulator of porcelain or the like suitably secured to the helmet, as for example, by means of screws extending from the interior of the helmet through apertures and threaded into tapped axial bores in the inner ends of the insulators. A resilient washer like the washer 34 shown in FIG. 4 is interposed between the lower end of each insulator support and the helmet in order to avoid chipping of the insulator upon contact with the hard metal surface of the helmet. As will be described more fully hereinafter the standoff support 20 serves to provide a feed connection to the ring 16.

The two ends of the discontinuous ring 16 extend into a substantially cylindrical housing 21 mounted on the exterior of the helmet 10. One end 22 of the discontinuous ring is electrically connected directly to the ground plane 13 by means of a conductor in the interior of the housing 21. This conductor also is electrically connected to a terminal 23 which extends through the aperture in the helmet and is accessible from the interior or bottom 11 to permit connection of one lead of a coaxial line leading to the receiving and transmitting equipment of the communication system carried by the operator at the mobile station.

The ungrounded or free end of the ring 16 is identified in FIG. 3 by the reference numeral 24. Since the frequency allocated for the operation of the communication system and the size of the helmet 10 may not permit use of a self-resonant antenna ring 16 having a length equal to approximately one-quarter wavelength of the assigned frequency, it may become desirable to employ an adjustable capacitor to permit tuning of the antenna to electrical resonance. This capacitor is identified in FIG. 3 by the reference numeral 25 and is electrically connected through a lead 26 and a terminal 27 to the free end 24 of the antenna ring. The capacitor 25 is preferably an air capacitor adjustable by turning a tuning screw 28 located at the top thereof. The other side of the capacitor remote from the terminal 27 is electrically connected to the ground plane 13 as is clearly indicated in FIG. 5. A top or cover for the housing 21 has an aperture therein normally closed by a plug 30 which plug may he removed to permit insertion of a screw driver in order to turn the screw 28 and, hence, to adjust the capacitor 25. The cover 29 is suitably secured to the outer end of the cylindrical housing 21. The inner end of the cylinder is sealed against the exterior of the helmet 10 by means of a sealing cement or the like so that the chamber formed by the housing is completely enclosed and is air tight.

A co-axial transmission line leading to the transmitting and receiving equipment of the mobile station is connected directly across the opening in the discontinuous ring 16. Any transmission line having a characteristic impedance of from 36 to 500 ohms may be used and, to provide a proper impedance match, a gamma type connection is employed. The impedance matching circuit consists of a section 31 of open wire transmission line formed between a short section 16a of the ring and the ground plane 13. The short section 16a, in accordance with an important feature of the present invention, is formed by the portion of the ring between the housing 21 and the standoff support 2i). The exact location of the support 20 is determined by the impedance of the coaxial line leading to the transmission and receiving equipment. Preferably, the feed point is selected so that the impedance match will remain substantially constant over a two to one frequency range. As is best shown in FIG. 4 one lead of the latter coaxial line is electrically connected to the terminal 23 while the other lead is connected to a terminal 32 accessible from the interior of the helmet and carried by the helmet in a position adjacent the standoff support 20. The terminal 32 is electrically insulated from the ground plane 13 and is connected by a conductor 33 extending through the interior of the standoff support 20 to the antenna ring 16, thus providing the feed connection. The ring 16 is suitably suspended within the support 20, for example, by means of a machine screw 35.

A second embodiment of the invention is illustrated in FIG. 6 where a combined helmet and antenna unit is shown which is similar to the unit illustrated in FIGS. 1 to 4 except for the fact that the helmet is formed of a hard, insulating plastic having a ground plane formed by a metal layer 14 covering much of the inner surface of the hat. The ground plane 14 is preferably formed by first coating the plastic base of the helmet with con ducting paint 15 containing particles such as silver and extending completely around the helmet in the area above the brim. A copper layer is then electroplated onto the conducting paint to form the ground plane 14. This ground plane may also be formed on the exterior surface of the hat but in either case, it is preferably spaced from the ring 16 by a distance equal to 2.5 degrees or less of the operating frequency. The supports 17, 18, 19 and 20, the ring 16, the housing 21 and the components mounted therein are all identical to the corre .5 spondingly numbered elements described above and shown in FIGS. 1 to 4. The schematic diagram shown in FIG. 5 is fully applicable to the antenna circuit formed by the unit shown in FIG. 6 since only the ground plane has been changed and this change has very little effect on the efiiciency of the antenna system itself.

In the form of the invention shown in FIG. 7 both a ground plane 50 and a discontinuous halo or ring antenna 51 are formed on the interior of the helmet, although it should be understood that either one of these rings or both of them could be formed on the exterior of the helmet, if desired, without changing the electrical characteristics of the antenna system. In the form shown, however, the ring 51 is formed by electro-plating a one-quarter inch strip having an open portion therein while the ground plane 50 is a closed loop'formed by electro-plating a continuous strip which is spaced from the ring 51 by a distance equal to 2.5 degrees or less of the operating frequency of the system. The electroplating of both rings is accomplished in the manner set forth above, that is, a conducting paint is first applied over the strips or areas to be covered and a copper layer is then electroplated onto the conducting paint. Electrical connections are then made to the discontinuous ring and the ground plane loop to form the circuit illustrated schematically in FIG. 5. Since these electrical connections will be obvious in view of the detailed description above they will not be described in detail.

A fourth embodiment of the invention is depicted in FIG. 8 and includes a helmet 58, similar in shape to the helmet described above, but formed of suitable material such as plastic. A combined antenna and ground plane unit 59 is detachably mounted on the helmet 58 as, for example, by means of screws (not shown) extending from the interior of the helmet and respectively threading into spaced apart supports or posts 62 forming part of the unit 59. The posts 62 also carry a discontinuous antenna ring 61 like the ring 16 described above and a continuous ground plane ring 60 spaced from the ring 61 by a distance equal to approximately 2.5 degrees or less of the operating frequency. The antenna ring 61 is connected at one end to the ground plane ring 60 by means of a strap or bus bar 63 and at the other end is connected through a variable capacitor 64 to the ground plane ring. A coaxial line 65 leading to the transmitting and receiving equipment has one lead 66 connected to the ground plane ring and has its other lead 67 connected to a suitable tap point on the antenna ring 61. The latter tap point is selected as described above to provide the desired impedance match. The rings of the unit 59 are disposed below the peak 68 of the helmet thus avoiding the safety problems discussed previously. Here again, the electrical circuit shown in FIG. 5 is applicable to the antenna construction shown in FIG. 8.

While the present invention has been described in connection with several illustrative embodiments it should be undestood that many modifications and changes will readily occur to those skilled in this art and it is, therefore, contemplated by the appended claims to cover any such modifications and changes as fall within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. Apparatus for use at a mobile station in radio communication systems, said apparatus comprising a hat adapted to be worn by the operator at the mobile station and having a top portion, a partially open antenna ring extending around the exterior of said hat at a position below said top portion, and conductor means extending around said hat over an area at least coextensive with said ring and spaced from said ring to form a ground plane for the antenna ring.

2. The apparatus defined by claim 1 wherein said conductor means is formed by electroplating said hat.

3. The apparatus defined by claim 2 wherein said con- 6 ductor means covers a substantial portion of the inner surface of the hat.

4. The apparatus defined by claim 1 wherein said conductor means is a narrow, closed loop formed on the surface of the hat.

5. The apparatus defined by claim 4 wherein said loop extends around the interior of the hat.

6. The apparatus defined by claim 4 wherein said loop is formed by electroplating a strip of conductive material.

7. The apparatus defined by claim 4 wherein said ring is also formed on a surface of the hat.

8. The apparatus defined by claim 7 wherein both the ring and the closed loop are formed on the interior of the hat.

9. The apparatus defined by claim 6 wherein said ring is also formed by electroplating a strip of conductive material onto a surface of said hat at a position spaced from said loop.

10. The apparatus defined by claim 9 wherein both the ring and the closed loop are formed on the interior of the hat.

11. The apparatus defined by claim 1 wherein an adjustable compacitor is connected between one end of the ring and the ground plane, wherein conducting means provides an electrical connection between the other end of said ring and the ground plane and wherein a feed connector is electrically connected to said ring at a point spaced a short distance from said other end.

12. The apparatus defined by claim 11 wherein said antenna ring and said conductor means are formed as a detachable unit, and means for detachably securing said unit to said hat.

13. The apparatus defined by claim 1 wherein said ring is spaced from said conductor means by a plurality of spaced apart supports protruding outwardly from said hat, at least one of said supports being partially hollow, and a feed connector disposed within the hollow portion of said one support connected to said ring.

14. The apparatus defined by claim 1 wherein an adjustable compacitor is connected between one end of the ring and the ground plane and wherein conducting means provides an electrical connection between the other end of said ring and said ground plane.

15. The apparatus defined by claim 14 wherein said antenna ring and said conductor means are formed as a detachable unit, and means to detachably secure said unit to said hat.

16. The appartus defined by claim 1 wherein said antenna ring and said conductor means are formed as a detachable unit, and means for detachably securing said unit to said hat.

17. Apparatus for use at a mobile station in radio communication systems, said apparatus comprising a hat adapted to be worn by the operator at the mobile station, conductor means extending around said hat and forming a ground plane, at least one support extending outwardly from the exterior of said hat, a partially open antenna ring mounted on said support and spaced from said ground plane, said support being at least partially hollow and a feed connector means disposed within the hollow portion of said support and connected to said ring.

18. The apparatus defined by claim 17 wherein an adjustable compacitor is connected between one end of the ring and the ground plane and wherein conducting means provides an electrical connection between the other end of said ring and said ground plane.

19. The apparatus defined by claim 17 wherein said conductor means is formed by electroplating said hat.

20. The apparatus defined by claim 19 wherein said conductor means covers a substantial portion of the inner surface of the hat.

21. The apparatus defined by claim 17 wherein said conductor means is a narrow closed loop formed on the surface of the hat.

22. The apparatus defined by claim 21 wherein said loop is formed by electroplating a strip of conducting material onto said surface of said hat.

References Cited by the Examiner UNITED STATES PATENTS Leeds et a1. 343-742 Sarles 343718 X Boyer 343742 LeFevre 343718 X Munk 343718 8 OTHER REFERENCES Boyer, Hula Hoop Antennas, Electronics, Ian. 11, 1963, pp. 4446.

5 Radar Helmet Helps Aircraft Spotters, Electronics,

October 1955, page 10;

ELI LIEBERMAN, Acting Primary Examiner.

m R. F. HUNT, Assistant Examiner. 

1. APPARATUS FOR USE AT A MOBILE STATION IN RADIO COMMUNICATION SYSTEMS, SAID APPARATUS COMPRISING A HAT ADAPTED TO BE WORN BY THE OPERATOR AT THE MOBILE STATION AND HAVING A TOP PORTION, A PARTIALLY OPEN ANTENNA RING EXTENDING AROUND THE EXTERIOR OF SAID HAT AT A POSITION BELOW SAID TOP PORTION, AND CONDUCTOR MEANS EXTENDING AROUND SAID HAT OVER AN AREA AT LEAST COEXTENSIVE WITH SAID RING AND SPACED FROM SAID RING TO FORM A GROUND PLANE FOR THE ANTENNA RING. 